As window manufacturers continue to improve the thermal performance of their products in order to achieve higher efficiency and energy savings, the trend is to replace the air inside of insulating glass (IG) units with inert gases that are heavier than air, including, but not limited to, Argon (Ar), Krypton (Kr), or a blend thereof. Since Argon and Krypton both have a higher density than air, they function as insulating gases that increase the insulating value of an IG unit. Air has a density of about 1.29 grams/liter (@ STP). In contrast, Argon has a density of about 1.78 grams/liter (@ STP) and currently has a cost in the range of $0.02 per liter, while Krypton has a density of about 3.74 grams/liter (@ STP) and currently has a cost in the range of $1.00 per liter. Although Argon and Krypton will both improve the thermal performance of an IG unit, Argon is typically used to its maximum efficiency in wider air spaces (½″ to ⅝″), and Krypton is typically used in narrower air spaces (¼″ to ⅜″).
Since both insulating gases, Argon and Krypton, are heavier than air, as the insulating gas fills the IG unit from the bottom thereof, the insulating gas pushes the lighter air gas to the top of the IG unit, and out of the enclosed air space of the IG unit. At some point in the filling process, there is a portion near the bottom of the IG unit that is mostly (above 90%) heavier than air gas (Argon, Krypton, or a mix of the two gases), and a portion near the top of the IG unit that is mostly air. Where the insulating gas interfaces with the air, there is a blended mixture of both air and the insulating gas. This blended mixture of gases is caused by convection, and dissipation of the insulating gas with the air it is replacing. For this reason, 150% to 500% of the injected insulating gas may be required to dilute the air volume in the IG unit down to less than 10% of what is remaining. A 90% fill rate has become an accepted standard in the IG fabrication industry.
The amount of time required to fill an IG unit with insulating gas (e.g., Argon, Krypton, or combination thereof) is affected by the following: (1) volume of air space in an IG unit; (2) flow rate of the injected insulating gas; (3) convection during the filling process (which is influenced by the flow rate); and (4) dissipation during the filling process (which is influenced by the time the gasses are exposed to each other).
To facilitate injection of a insulating gas into the space between glass panes (also known as “glass lites”) of an IG unit, one or two openings or holes may be provided in the spacer that separates two adjacent glass panes. For IG units with spacers having a single hole, the hole is located at or near a corner of the IG unit. To inject insulating gas into the space between glass panes, the IG unit is typically positioned in a vertical orientation, with the hole positioned at, or near, the highest point of the IG unit. Existing “single hole” gas filling processes can take several different forms, including, but not limited to: (1) vacuum fill, (2) fast fill, and (3) slow fill (single hole) processes, which will now be described.
Vacuum fill: Vacuum filling happens when the entire IG unit (or multiple IG units) is inserted into a vacuum chamber. Over a period of time, most of the air is extracted from the space (i.e. “interpane” space) between glass panes (depending on desired fill rate), and then replaced by the desired insulating gas. Although this method is reliable, it is expensive to implement. In this respect, a vacuum chamber has fixed dimensions, and thus multiple vacuum chambers are needed to accommodate IG units of different sizes. If the vacuum chamber is too large for the TO unit, then a high percentage of insulating gas is wasted as it fills the space inside the vacuum chamber, but outside of the IG unit. The energy cost to operate a vacuum chamber is also high. For several of the above reasons, the vacuum fill method is not practical for fabrication of custom size IG units, or fabrication of standard size IG units in a just-in-time (HT) manufacturing environment.
Fast Fill: In order to minimize the fill time (resulting in reduced labor cost, as well as increased capacity) fast fill machines utilize a probe that is inserted into an IG unit and injects gas at a high rate (e.g., 6 to 10 liters per minute) from a first portion of the probe, while suctioning out exhaust gas at a second portion of the probe at substantially the same rate as the injection rate. This fast fill process not only causes convection, but encourages it. Since the gasses are mixed, the suctioned exhaust gas is passed through an oxygen sensor that monitors the concentration of oxygen therein. Since oxygen is roughly 115 of air (20.9%), the fast fill machine can be programmed to stop injecting gas when the oxygen concentration of the suctioned exhaust gas reaches a predetermined target concentration (e.g., approximately 0.9% oxygen, to achieve 90% insulating gas within the IG unit). The advantage of the fast fill process is that it reduces labor costs, increases capacity, and is suitable for both the fabrication of custom size IG units and the fabrication of standard size IG units in a just-in-time (JIT) manufacturing environment. A serious disadvantage of the fast fill process is that it wastes a significant amount of insulating gas (i.e., 200% to 500%). This waste of insulating gas makes the fast fill process impractical for injecting the relatively expensive Krypton gas.
Slow fill (single hole): The slow fill (single hole) process involves the insertion of a probe, or tube through a hole at the top of the IG unit, with the tube extending to the lowest portion of the IG unit. If the insulating gas is injected at a slow rate, convection is minimized, thereby reducing the amount of insulating gas that is wasted. This is beneficial where a relatively expensive insulating gas (such as Krypton) is being used. An advantage of the slow fill (single hole) process is the reduced insulating gas loss (typically 70% at an injection rate of 3 liters per minute, and less than 35% at an injection rate of 1 liter per minute). Disadvantages of the slow fill (single hole) process are higher labor costs, higher capital costs, and greatly reduced capacity due to the lengthened fill time.
To fill IG units with spacers having two holes or openings, the IG unit is typically positioned in a vertical orientation, with the first hole located proximate to the top of the IG unit and the second hole located proximate to the bottom of the IG unit. Existing “two holes” gas filling processes can take several different forms, including, but not limited to methods 1 and 2 described below.
Method 1: A first probe is inserted into the bottom hole of the IG unit for injection of the insulating gas. As discussed above, both Argon and Krypton are heavier than air, and thus injection of these gasses into the bottom of the IG unit minimizes the convection of these gasses with the air they are replacing. The injection rate of the insulating gas can be increased to minimize time, or reduced to minimize waste. A second probe is inserted into the top hole of the IG unit to suction exhaust gas from the IG unit. Injection of the insulating gas is stopped when the oxygen concentration of the suctioned exhaust gas reaches a target concentration.
Method 2: In this method, only one probe is used. The probe is inserted into the bottom hole of the IG unit. Since the insulating gas is heavier than air, it will displace air with predictable convection and dissipation, at different flow rates. This process uses a timer that is set based upon the flow rate, convection, dissipation, and predictable waste. This method is suitable when Argon is the insulating gas, since an intentional overfill is not costly. However, when an expensive insulating gas (such as Krypton) is used, this method requires a balancing between waste of the expensive insulating gas and the need to fill the IG unit to a prescribed minimum level.
The present invention provides a method and apparatus for filling insulating glass units with insulating gas that overcomes drawbacks of the prior art, and provides additional advantages.